This invention relates generally to electronic controls for controlling the starting, running and stopping of motors, and more particularly to capstan and reel drive motors and circuitry therefor as used in recording and reproducing digital information on tape.
The recording and reproduction of information on recording tape in industry has been increasing at a tremendous rate. There is a growing need for providing such recording and reproduction systems at low cost. Problems associated with providing low cost systems are that in order for the recorded tape to be played on different reproduction systems, it must be recorded at substantially the same speed. Many prior art arrangements exist for controlling the speed at which tape is run off a payoff reel and wound up on a winding reel. Generally this has involved controlling the speeds of the individual motors driving the payoff and winding reels. One common way for controlling the speeds of the winding and payoff reels employs a capstan and pinch wheel arrangement for driving the tape. By regulating the rotational speed of the capstan motor, one regulates the linear rate at which the tape moves past the recording and reproduction heads. In such an arrangement it is necessary to control the peripheral velocity of the reels to be identical to that of the capstan. One way of maintaining the capstan motor speed constant is to regulate the CEMF (counter-electromotive force) developed by this motor and to maintain a predetermined tension on the winding and payoff reels by controlling the armature motor current associated with the payoff and winding reels. The latter controls the torque delivered by the motors and hence the tension in the tape. One way of substantially reducing the costs involved in the manufacture of drive systems for a tape recorder and reproducer, i.e. tape transports, is to employ less expensive adjustable speed DC motors to drive the reels. Unfortunately when this is done, certain difficulties are encountered. Starting, stopping and running characteristics of inexpensive motors may vary from one motor to another in an undesirable manner because of differing motor armature resistance. Also, the inexpensive motors tend to have relatively higher rotational friction. Because of this, the torque delivered to the reels by the motors will vary differently for different motors. The consequences of such undesirable motor characteristics, if not accommodated, is that tape may be unduly stressed and break, or a loop of tape caused to accumulate which could foul up tape movement or result in tape breakage when the tape is suddenly tensioned at the instant the slack is eliminated.
Accordingly, it is one object of this invention to provide an improved motor drive system for recording and reproducing devices which will enable the use of less expensive motors.
It is another object of this invention to accommodate adjustable speed DC motors and enable them to operate in recording and reproduction devices in an acceptable manner.
It is another object of this invention to provide an improved arrangement for reeling ribbon on and/or off a spool.
It is another object of the present invention to provide an improved tape transport comprising only a single capstan motor and two low cost reel motors.
It is another object of this invention to provide improved capstan and reel motor drive circuitry for coordinated starting and stopping, as well as improved circuitry for increasing the torque applied to the winding reel as its diameter increases.
Another object of this invention is to provide improved tape transport control circuitry for controlling tension on tape being driven along its length by a first motor of relatively high quality and being accumulated on a winding reel driven by a winding motor and paid off a payoff reel driven by a payoff motor during starting, running and stopping.
Another object of this invention is to provide improved tape transport circuitry that is easily utilized to operate in a fast wind/rewind (forward/reverse) mode with controlled inter-reel tension during starting, running and stopping.
A further object of this invention is to provide improved tape transport circuitry in which the tape drive motor parameters are used as a reference for the winding and payoff reel motor drives to reflect load changes to the reels, which load changes include the reflection of starting and running conditions to the winding reel motor and stopping conditions to the payoff reel motor.
Still another object of this invention is to provide improved tape transport control circuitry via a regulator which is a current regulator at read/write speeds and which automatically converts into a terminal voltage regulator at fast wind/rewind (forward/reverse) speeds.
Still another object of the invention is to provide an improved motor control employing regenerative drag in the payoff reel for course speed regulation at fast wind/rewind (forward/reverse) speeds.